Engineering Graphics Stephen W. Crown Ph.D. Multiview Sketches Engineering Graphics Stephen W. Crown Ph.D.

Objective How to use sketching as an effective tool in the engineering design process How to represent a 3-D object effectively on a 2-D drawing surface (multiview sketching)

Overview Sketching Mechanics of sketching Multiview sketches Definition Tools / Instruments Mechanics of sketching Lines and Curves A Bounding Box Multiview sketches How to create them When to use them Why use sketches? Creativity Communication Documentation

Sketching Definition: A rough freehand drawing used to document, communicate, and refine ideas developed in the ideation phase of the design process Beginners will benefit from instruments Follows standard practices A developed skill Should be the first step of any CAD drawing

Tools Pencils Paper Eraser Use a mechanical pencil (0.5mm lead) Practice using different pressure to produce desired linetypes (construction lines) Paper Unlined paper is the most useful Square grid and tracing paper is often useful Eraser A good eraser is worth the investment Do not overuse your eraser (save some mistakes)

Using Simple Instruments The use of mechanical instruments is recommended only for beginners. Break away from reliance on tools that slow you down. Helpful tools for beginners Compass Triangles Dividers Ruler

Mechanics of Sketching Drawing straight lines Drawing curved lines Using a bounding box

Drawing straight lines Mark starting and ending point Break long lines into short line segments by marking the midpoint Start with a light pass if necessary and then darken Use a loose comfortable grip Reorient the paper to your convenience test your skill with different orientations an awkward orientation may occasionally produce positive results

Drawing curved lines Break large arcs/circles into small segments Make guide marks for each segment Circles and Ellipses Sketch a light square/rectangle Lightly sketch in diagonals Mark contact points on square/rectangle Rotate the paper for each segment

Bounding Box and Construction Lines Plan choose proper scale and orientation don’t crowd sketches Start with a bounding box Use light straight construction lines Draw boundary lines of internal features starting with the largest features Sketch dark object lines using light boundary lines as a guide

Multiview Sketching Represents a 3-D object with a series of 2-D views in contrast to “pictorials” which show all three dimensions in a single view Also called orthographic projection Best understood by engineers or technically trained people Multiview Drawing Pictorial

Parallel projection Preserves true relationship between features The geometry is generally not distorted Lines that are parallel on the object are parallel on the drawing Parallel projectors The object is projected onto a projection plane as a shadow is projected where the rays form the light source are parallel. Projection from one view to another is accomplished with parallel projection lines

Parallel versus Perspective Projection

Projection Planes versus Views Object formed from projection lines projected perpendicularly onto a projection plane Planes: Horizontal, frontal, and profile Each projection plane is perpendicular to adjacent projection planes Principle views The object is rotated 90 degrees about the horizontal or vertical axis to give six principle views (top, bottom, front, rear, left, and right side) Common views: top, front, and right side

Only use Necessary Views One view drawings Stamped, thin or extruded parts Specify thickness with a note Two view drawings Cylindrical parts Show the circular and rectangular view Three view drawings Usually sufficient for all other drawings Top, front, and right side view

Orientation and Placement of Views The most descriptive view should be selected as the front view The natural orientation of the part should be preserved if possible Views must be aligned Top view above front view Right view to the right of front view

Hidden lines Represented with dashed lines Precedence of lines (visible, hidden, center) Views should be selected to minimize the use of hidden lines most descriptive view should be selected as the front view

First Versus Third Angle Projection Third Angle Projection Associated with English units First Angle Projection Associated with SI units ANSI Symbol

Fold Lines Represents a 90 degree fold between views Generally not shown on engineering drawings except when views other than the principle views (auxiliary views) are used. Labeled as: H/F, F/P, F/1, 1/2

Terminology to Relate Views Adjacent view A view that is separated by a fold line The top view is an adjacent view to the front view Central View A view that is between two adjacent views The front view is the central view of the top, front, and right side view Related views Two views that are adjacent to a central view The top and right side view are related views since they are both adjacent to the front view

Constructing a New View 2 The top and front views of a surface are shown The fold line represents a 90 degree fold between the views Parallel projection lines are perpendicular to the fold line 1 3 1 3 2

Constructing a New View A vertical fold line is drawn at an arbitrary distance from the front view Parallel projection lines are drawn from each vertex The common depth between the top and side view is used to locate each vertex on the projection lines 1 2 3

Sketching as Part of the Creative Design Process Quickly translate thoughts to paper An effective means of communication Stimulates creativity and visualization

Sketching Allows for the Quick Translation of Thoughts to Paper Commit thoughts to paper before you lose an idea Avoid the of use mechanical tools (drawing tools are helpful for beginners) Does not need to be an exact representation objects may be simplified parts may be missing Avoid erasing as new ideas are developed make new sketches start with light lines and then darken with darker lead or heavier strokes

Sketching is An Effective Means of Communication Understand your audience Who is looking at the sketches? What details are they interested in? What type of sketch will they best understand? Follow standard practices You may not always accompany your sketches Others may misinterpret your drawing Sketches provide a log of ideas that were considered in a brainstorming session

Sketching Stimulates Creativity and Helps Visualization The process of sketching ideas that are partially developed often aids the design process do not wait until you have a clear picture before you start sketching allow yourself the freedom to make mistakes Visualization of the entire design is essential but often impossible without aid of sketches

Appendix Engineering Graphics

Make a Quick Sketch You will have ten seconds to make a sketch of each object shown below before being asked a few questions about the objects. How many of the nine views consisted of a square bounding box? How many of the nine views are the same? How many of the nine views consisted of only vertical or horizontal lines? What is the volume of each object (Cube=8 in3)?